George M. Sheldrick

Bio: George M. Sheldrick is an academic researcher from University of Göttingen. The author has contributed to research in topics: Crystal structure & Bond length. The author has an hindex of 58, co-authored 791 publications receiving 151229 citations. Previous affiliations of George M. Sheldrick include University of Regensburg.

Cyclisierung von (Fluorsilyl)phosphanen zu 1,3‐Diphospha‐2,4‐disilacyclobutanen – Kristallstrukturuntersuchungen

Abstract: Lithiiertes tert-Butylphosphan reagiert mit Di-tert-butyldifluorsilan und Difluorbis[methyl(trimethylsilyl)amino]silan zu den (Fluorsilyl)phosphanen 1 und 2 sowie zum (Di-tert-butylsilandiyl)-bisphosphan 3. Die cyclischen Verbindungen 4 und 5 werden durch die Umsetzung von 1 und 2 mit tert-C4H9Li erhalten. Dilithiiertes 3 reagiert mit Dichlorphenylphosphan zum 1,2,3-Triphospha-4-silacyclobutan 6. Nach Kristallstrukturanalysen besitzen 4 und 5 jeweils planare Si2P2-Ringe mit SiP-Bindungen zwischen 224.1(1) und 228.0(1) pm. Cyclisation of (Fluorsilyl)phosphanes to 1,3-Diphospha-2,4-disilacyclobutanes – Crystal Structure Determinations Lithiated tert-butylphosphane reacts with di-tert-butyldifluorosilane and with difluorobis[methyl(trimethylsilyl)amino]silane to give the (fluorosilyl)phosphanes 1 and 2 as well as the (di-tert-butylsilanediyl)bisphosphane 3. The cyclic compounds 4 and 5 are obtained in the reaction of 1 and 2 with tert-C4H9Li. Dilithiated 3 reacts with dichlorophenylphosphane to form the 1,2,3-triphospha-4-silacyclobutane 6. According to crystal structure analyses, 4 and 5 contain planar Si2P2 rings with SiP bonds between 224.1(1) and 228.0(1) pm.

Crystal structure of polymeric tris(trimethyltin) chromate hydroxide

Abstract: Crystals of the title compound are orthorhombic, space group Pbca, a= 20·85(2), b= 11·55(2), c= 16·58(2)A(at ca. –30 °C), Z= 8. The structure was determined at ca. –30 °C from diffractometer data by direct methods and refined by full-matrix least-squares to R 0·045 for 488 unique observed reflexions. The structure consists of a complicated network polymer. There are three crystallographically independent and approximately planar tri-methyltin groups, and in each case, approximately trigonal bipyramidal co-ordination of the tin atom is completed by two axial oxygen atoms. Each oxygen atom in the chromate group is also bonded to tin, and the hydroxide group bridges two trimethyltin groups and is probably hydrogen bonded to one of the chromate oxygens. The two tin atoms linked by the hydroxide group have similar co-ordination geometries, with short Sn–O(H)[2.l4(3) and 2·17(4)A] and long Sn–O(Cr)[2·48(5) and 2·51(4)A]. The two oxygen atoms responsible for the long Sn–O bonds make the shortest two Cr–O bond lengths [1·61(4) and 1·56(4)A]. Other bond lengths and angles are : Sn–O, 2·16(4) and 2·29(4); Cr–O, 1·78(4) and 1·70(4); mean Sn–C, 2·13 A; mean C–Sn–C, 119; mean O–Sn–O, 176; mean Cr–O–Sn, 144; and Sn–O–Sn, 136(2)°.

Atomic resolution structure of squash trypsin inhibitor: unexpected metal coordination.

Abstract: CMTI-I, a small-protein trypsin inhibitor, has been crystallized as a 4:1 protein–zinc complex. The metal is coordinated in a symmetric tetrahedral fashion by glutamate/glutamic acid side chains. The structure was solved by direct methods in the absence of prior knowledge of the special position metal centre and refined with anisotropic displacement parameters using diffraction data extending to 1.03 A. In the final calculations, the main-chain atoms of low Beq values were refined without restraint control. The two molecules in the asymmetric unit have a conformation that is very similar to that reported earlier for CMTI-I in complex with trypsin, despite the Met8Leu mutation of the present variant. The only significant differences are in the enzyme-binding epitope (including the Arg5 residue) and in a higher mobility loop around Glu24. The present crystal structure contains organic solvent molecules (glycerol, MPD) that interact with the inhibitor molecules in an area that is at the enzyme–inhibitor interface in the CMTI-I–trypsin complex. A perfectly ordered residue (Ala18) has an unusual Ramachandran conformation as a result of geometrical strain introduced by the three disulfide bridges that clamp the protein fold. The results confirm deficiencies of some stereochemical restraints, such as peptide planarity or the N—Cα—C angle, and suggest a link between their violations and hydrogen bonding.

A short history of SHELX

Abstract: An account is given of the development of the SHELX system of computer programs from SHELX-76 to the present day. In addition to identifying useful innovations that have come into general use through their implementation in SHELX, a critical analysis is presented of the less-successful features, missed opportunities and desirable improvements for future releases of the software. An attempt is made to understand how a program originally designed for photographic intensity data, punched cards and computers over 10000 times slower than an average modern personal computer has managed to survive for so long. SHELXL is the most widely used program for small-molecule refinement and SHELXS and SHELXD are often employed for structure solution despite the availability of objectively superior programs. SHELXL also finds a niche for the refinement of macromolecules against high-resolution or twinned data; SHELXPRO acts as an interface for macromolecular applications. SHELXC, SHELXD and SHELXE are proving useful for the experimental phasing of macromolecules, especially because they are fast and robust and so are often employed in pipelines for high-throughput phasing. This paper could serve as a general literature citation when one or more of the open-source SHELX programs (and the Bruker AXS version SHELXTL) are employed in the course of a crystal-structure determination.

Crystal structure refinement with SHELXL

Abstract: The improvements in the crystal structure refinement program SHELXL have been closely coupled with the development and increasing importance of the CIF (Crystallographic Information Framework) format for validating and archiving crystal structures. An important simplification is that now only one file in CIF format (for convenience, referred to simply as `a CIF') containing embedded reflection data and SHELXL instructions is needed for a complete structure archive; the program SHREDCIF can be used to extract the .hkl and .ins files required for further refinement with SHELXL. Recent developments in SHELXL facilitate refinement against neutron diffraction data, the treatment of H atoms, the determination of absolute structure, the input of partial structure factors and the refinement of twinned and disordered structures. SHELXL is available free to academics for the Windows, Linux and Mac OS X operating systems, and is particularly suitable for multiple-core processors.

OLEX2: a complete structure solution, refinement and analysis program

Abstract: New software, OLEX2, has been developed for the determination, visualization and analysis of molecular crystal structures. The software has a portable mouse-driven workflow-oriented and fully comprehensive graphical user interface for structure solution, refinement and report generation, as well as novel tools for structure analysis. OLEX2 seamlessly links all aspects of the structure solution, refinement and publication process and presents them in a single workflow-driven package, with the ultimate goal of producing an application which will be useful to both chemists and crystallographers.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

PHENIX: a comprehensive Python-based system for macromolecular structure solution

Abstract: Macromolecular X-ray crystallography is routinely applied to understand biological processes at a molecular level. How­ever, significant time and effort are still required to solve and complete many of these structures because of the need for manual interpretation of complex numerical data using many software packages and the repeated use of interactive three-dimensional graphics. PHENIX has been developed to provide a comprehensive system for macromolecular crystallo­graphic structure solution with an emphasis on the automation of all procedures. This has relied on the development of algorithms that minimize or eliminate subjective input, the development of algorithms that automate procedures that are traditionally performed by hand and, finally, the development of a framework that allows a tight integration between the algorithms.